Fuel injection system for an internal combustion engine

ABSTRACT

In a fuel injection system for an internal combustion engine, having a fuel high-pressure reservoir, from which an injection line for the fuel to be injected and a drive line for fuel branch off, which fuel is used as a working medium, the fuel is intended to be utilized, in a simple way, in order to furnish a working medium at high pressure that can be used for additional functions. To that end, at least one converter is provided, which is connected to the drive line and in which a volumetric flow of the fuel, which is under pressure, is converted into a volumetric fuel of a working medium which is under pressure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/02408 filed onJul. 22, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel injection system for an internalcombustion engine, having a fuel high-pressure reservoir, from which aninjection line for the fuel to be injected and a drive line for fuelbranch off, which fuel is used as a first working medium.

2. Description of the Prior Art

One fuel injection system of the type with which the invention isconcerned is already known from German Patent Disclosure DE 44 07 585 A1and is based on an injection system known by the name “common rail”. Inthis injection system, a cylindrical pressure container is used, towhich fuel is delivered by a high-pressure pump. The high-pressurereservoir serves essentially as a buffer, which damps pressurefluctuations that result from the delivery of the fuel by thehigh-pressure pump and the withdrawal of the fuel by the injectionnozzles.

From the above reference, it is known for the fuel present in thehigh-pressure reservoir to be used for actuating a hydraulic valvecontroller. To that end, the fuel is first delivered by the drive lineto a hydraulic chamber, with which an outlet valve is associated andwhich is controlled by two control valves, and then to a hydraulicchamber which is associated with an inlet valve and is also controlledby two control valves. By suitable switching of the control valves, theinlet valve and the outlet valve are opened counter to the action of aconventional valve spring and closed again by means of the valve spring.

SUMMARY OF THE INVENTION

The fuel injection system according to the invention, has the advantagethat an external consumer, which is actuated not with the fuel itselfbut rather with an arbitrary other, second working medium, can beconnected to the high-pressure reservoir. The converter makes itpossible to put the second working medium under a pressure that differsfrom the fuel pressure.

In one advantageous embodiment of the invention, it is provided that theconverter has a translationally displaceable inlet piston and anactuator, by which the inlet piston can be acted upon periodically byfuel under pressure. In this way, at little structural expense, it ispossible for the potential energy stored in the fuel under pressure tobe converted into a reciprocating motion of the inlet piston, which canthen in turn be converted into a volumetric flow of a second workingmedium that is under pressure.

Preferably, it is provided that the actuator is a 3/2-way valve. Suchvalves are available in the form of reliable mass-produced components,making the expense for controlling the inlet piston minimal.

In a preferred embodiment of the invention, it is also provided that theconverter has a translationally displaceable outlet piston, which isconnected to the inlet piston, and two check valves associated with theoutlet piston. The outlet piston acts on the order of a piston pump thatis driven directly by the inlet piston. Thus a loss- free conversion ofthe driving energy furnished by the inlet piston is obtained.

Preferably, the cross section of the inlet piston differs from the crosssection of the outlet piston. In this way, a conversion of the pressureof the fuel, which is used as a first working medium, into a higher orlower pressure of a second working medium can be attained. For instance,if the cross section of the inlet piston is smaller than the crosssection of the outlet piston, then a lesser pressure in the secondworking medium and a higher volumetric flow, compared to the fuel, areattained. Conversely, if the cross section of the inlet piston isgreater than the cross section of the outlet piston, a higher pressurethan in the fuel can be attained in the second working medium, althoughin that case a lesser volumetric flow is available.

In a preferred feature of the invention, a high-pressure reservoir forthe second working medium can be provided. This high-pressure reservoirfunctions similarly to the fuel high-pressure reservoir, in thatpressure fluctuations resulting from the delivery of second workingmedium to its reservoir are damped. Furthermore, withdrawal of thesecond working medium from its reservoir also leads to only a negligiblepressure change in this reservoir, so that this reservoir furnishes thesecond working medium at an essentially constant pressure.

Furthermore, two converters can be provided, which operate inalternation. In this way, pulsation of the pressure in the secondworking medium can be further reduced, since a virtually constantpumping of the second working medium is attainable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully described below with specific referenceto the drawings, in which:

FIG. 1, is a schematic view, of a first embodiment of a fuel injectionsystem according to the invention in a first embodiment; and

FIG. 2, is a schematic view, similar to FIG. 1 and showing an alternateembodiment of a fuel injection system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing in detail, FIG. 1 schematically shows afuel injection system in a first embodiment of the invention. Itincludes a high-pressure reservoir 10 for fuel, which is used to operatean internal combustion engine, not shown. The fuel is delivered to thehigh-pressure reservoir 10 through a delivery line 12, whichcommunicates with a high-pressure pump, not shown. From thehigh-pressure reservoir 10, an injection line 14 for the fuel branchesoff and leads to the individual injection nozzles of the injectionsystem.

Also branching off from the fuel high-pressure reservoir 10 is a driveline 16, by means of which fuel, which is used as first working medium,can be withdrawn from the high-pressure reservoir.

A converter 18, which comprises an actuator 20 and a piston pump 22, isconnected to the drive line 16.

The actuator 20 is a 3/2-way valve, which has one inlet 24, whichcommunicates with the drive line 16, and one outlet 26, communicatingwith the piston pump 22, as well as another outlet 28, which returns toa fuel reservoir. The actuator 20 furthermore has a valve drivemechanism 30, which is capable of translationally adjusting a valveslide 32.

The piston pump 22 has a translationally displaceable inlet piston 34,which is connected to the outlet 26 of the actuator 20, and atranslationally displaceable outlet piston 36, which is solidlyconnected to the inlet piston 34. A drain line 37 for a leakage flowbranches off from an interstice between the inlet piston 34 and theoutlet piston 36. A compression spring 38 is braced on the outlet piston36 and urges the inlet piston and the outlet piston into a position inwhich the piston pump volume associated with the inlet piston 34 andcommunicating with the outlet 26 is minimal.

The outlet piston 36 is assigned a working volume into which a deliveryline 39 for the second working medium discharges. A check valve 40 isdisposed in the delivery line 39. An outlet line 41, in which a checkvalve 42 is disposed, branches off from the working volume associatedwith the outlet piston 36. The outlet line 41 leads to a high-pressurereservoir 44 for the second working medium. From the high-pressurereservoir 44, the second working medium can be delivered to a consumerthrough a withdrawal line 46.

A sensor 43 is mounted on the piston pump 22 and measures both thetravel of the inlet piston and the outlet piston and the pressure. Thesedata are made available to the valve drive mechanism 30.

The injection system described, with the converter 18, functions asfollows: The valve drive mechanism 30 controls the valve slide 32 insuch a way that the inlet piston 34 is periodically acted upon by thefuel under pressure from the high-pressure reservoir 10. In the process,the outlet piston 36 is adjusted downward each time in terms of FIG. 1,and as a result of that, the second working medium is pumped from thedelivery line 39 into the outlet line 41 and from there into thehigh-pressure reservoir 44 for the second working medium. The sensor 43in this process assures that predetermined values for the stroke of theinlet piston and the outlet piston and for the pressure are adhered to.By the choice of the cross section of the inlet piston 34 relative tothe outlet piston 36, the fuel pressure prevailing in the high- pressurereservoir 10 can be converted into a pressure of the second workingmedium in the high-pressure reservoir 44 which is different from thepressure in the reservoir 10. At the ratio of the cross sections shownin FIG. 1, a high pressure of the fuel in the high-pressure reservoir 10is converted into a somewhat lower pressure in the second working mediumhigh-pressure reservoir 44, since the cross section of the inlet piston34 is less than the cross section of the outlet piston 36. Virtually anyarbitrary medium can be used as the second working medium, in particularoil or water. The type of second working medium used depends on theparticular application.

From the drive line 16, a further drive line 16′ branches off, leadingto a further converter 18′. In its design and mode of operation, thisconverter is equivalent to the converter 18, with the sole distinctionthat it operates in phase displacement with the first converter 18. Inother words, if the inlet piston 34 of the first converter 18 is justnow being acted upon by pressure, so that it is adjusted counter to theaction of the compression spring 38, then the inlet piston 34′ is justat the same time not acted upon by pressure, so that it is returned bythe compression spring 38′. In this way, the second working medium isdelivered to the reservoir 44 in a substantially uniform way, so thatthe resultant pressure fluctuations in the high-pressure reservoir 44are only slight.

The described construction thus makes it possible, at comparativelylittle effort or expense, to utilize the fuel under pressure in thehigh-pressure reservoir 10 as a first working medium in order to furnisha second working medium in a high-pressure reservoir 44 at highpressure. This second working medium can be used for an arbitraryadditional function.

In FIG. 2, a simplified embodiment of the system shown in FIG. 1 isshown. Unlike the embodiment shown in FIG. 1, in the embodiment of FIG.2 only a single converter 18 is used. In addition, no high-pressurereservoir 44 is provided between the second check valve 42 and thewithdrawal line 46; in other words, the second working medium isdelivered directly to the consumer. This embodiment is especially wellsuited to quickly furnishing the second working medium, for instance fora safety function.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

I claim:
 1. In a fuel injection system for an internal combustionengine, having a fuel high-pressure reservoir (10), from which aninjection line (14) for the fuel to be injected and a drive line (16;16′) for fuel branch off, which fuel is used as a first working medium,the improvement wherein at least one converter (18; 18′) is provided,which is connected to the drive line (16; 16′) and in which a volumetricflow of the fuel, which is under pressure, is converted into avolumetric flow of a second working medium which is under pressure,wherein a high-pressure reservoir (44) for the second working medium isprovided.
 2. The fuel injection system of claim 1, wherein the converter(18; 18′) has a translationally displaceable inlet piston (34; 34′) andan actuator (20; 20′), by which the inlet piston can be acted uponperiodically by fuel under pressure.
 3. The fuel injection system ofclaim 2, wherein the actuator is a 3/2-way valve (20; 20′).
 4. The fuelinjection system of claim 9, wherein the converter (18; 18′) has atranslationally displaceable outlet piston (36; 36′), which is connectedto the inlet piston (34; 34′), and two check valves (40, 42; 40′, 42′)associated with the outlet piston.
 5. The fuel injection system of claim4, wherein the cross section of the inlet piston (34; 34′) differs fromthe cross section of the outlet piston (36; 36′).
 6. The fuel injectionsystem of claim 1, wherein two converters (18; 18′) are provided, whichoperate in alternation.
 7. The fuel injection system of claim 3, whereinthe converter (18; 18′) has a translationally displaceable outlet piston(36; 36′), which is connected to the inlet piston (34; 34′), and twocheck valves (40, 42; 40′, 42′) associated with the outlet piston. 8.The fuel injection system of claim 7, wherein the cross section of theinlet piston (34; 34′) differs from the cross section of the outletpiston (36; 36′).
 9. The fuel injection system of claim 2, wherein twoconverters (18; 18′) are provided, which operate in alternation.
 10. Thefuel injection system of claim 3, wherein two converters (18; 18′) areprovided, which operate in alternation.
 11. The fuel injection system ofclaim 4, wherein two converters (18; 18′) are provided, which operate inalternation.
 12. The fuel injection system of claim 5, wherein twoconverters (18; 18′) are provided, which operate in alternation.
 13. Thefuel injection system of claim 8, wherein two converters (18; 18′) areprovided, which operate in alternation.
 14. The fuel injection system ofclaim 5, wherein two converters (18; 18′) are provided, which operate inalternation.